package unit;

/**
 * Regression test for hibernate-0001/0002/0003/0004/0005: CWE-407 O(n²) membership
 * tests in Hibernate ORM mapping layer.
 *
 * These tests use a synthetic stand-in (not the real Hibernate classes) to demonstrate
 * the O(n²) vs O(n) performance difference and confirm the fix semantics.
 *
 * Defects confirmed at:
 *   hibernate-0001: Constraint.addColumn()            — ArrayList.contains() inside loop
 *   hibernate-0002: ForeignKey.addReferencedColumn()  — ArrayList.contains() inside loop
 *   hibernate-0003: Index.addColumn()                 — ArrayList.contains() inside loop
 *   hibernate-0004: buildRecursiveOrderedFkSecondPasses() — ArrayList.contains()+add(0,...) in recursion
 *   hibernate-0005: orderHierarchy()                  — ArrayList.contains() in recursive hierarchy sort
 */
public class HibernateConstraintColumnTest {

    // ---- Defective model (mirrors Hibernate before fix) ----

    static class DefectiveConstraint {
        private final java.util.ArrayList<String> columns = new java.util.ArrayList<>();

        public void addColumn(String column) {
            if (!columns.contains(column)) {  // O(n) — CWE-407
                columns.add(column);
            }
        }

        public java.util.List<String> getColumns() {
            return columns;
        }
    }

    // ---- Fixed model (mirrors Hibernate after fix) ----

    static class FixedConstraint {
        private final java.util.LinkedHashSet<String> columns = new java.util.LinkedHashSet<>();

        public void addColumn(String column) {
            columns.add(column);  // O(1) — dedup handled by set
        }

        public java.util.List<String> getColumns() {
            return new java.util.ArrayList<>(columns);
        }
    }

    // ---- Defective FK second-pass ordering ----

    static class DefectiveOrderedList {
        private final java.util.List<String> ordered = new java.util.ArrayList<>();

        public void addIfAbsent(String item) {
            if (!ordered.contains(item)) {  // O(n) — CWE-407
                ordered.add(0, item);        // O(n) prepend
            }
        }

        public java.util.List<String> getOrdered() {
            return ordered;
        }
    }

    // ---- Fixed FK second-pass ordering ----

    static class FixedOrderedList {
        private final java.util.LinkedHashSet<String> ordered = new java.util.LinkedHashSet<>();

        public void addIfAbsent(String item) {
            ordered.add(item);  // O(1)
        }

        public java.util.List<String> getOrdered() {
            return new java.util.ArrayList<>(ordered);
        }
    }

    // ---- Tests ----

    public static void main(String[] args) {
        testConstraintDedup();
        testOrderedListDedup();
        testPerformance();
        System.out.println("All hibernate CWE-407 unit tests passed.");
    }

    static void testConstraintDedup() {
        DefectiveConstraint defective = new DefectiveConstraint();
        FixedConstraint fixed = new FixedConstraint();

        for (int i = 0; i < 100; i++) {
            defective.addColumn("col" + (i % 10));
            fixed.addColumn("col" + (i % 10));
        }

        // Both should deduplicate to exactly 10 unique columns
        assert defective.getColumns().size() == 10
            : "Defective: expected 10 unique columns, got " + defective.getColumns().size();
        assert fixed.getColumns().size() == 10
            : "Fixed: expected 10 unique columns, got " + fixed.getColumns().size();

        // Both should preserve insertion order of first occurrence
        assert defective.getColumns().get(0).equals("col0") : "Defective: wrong order";
        assert fixed.getColumns().get(0).equals("col0") : "Fixed: wrong order";

        System.out.println("  [PASS] constraint column dedup (defective=" + defective.getColumns().size()
            + " fixed=" + fixed.getColumns().size() + ")");
    }

    static void testOrderedListDedup() {
        DefectiveOrderedList defective = new DefectiveOrderedList();
        FixedOrderedList fixed = new FixedOrderedList();

        String[] items = {"table_c", "table_a", "table_b", "table_c", "table_a", "table_d"};
        for (String item : items) {
            defective.addIfAbsent(item);
            fixed.addIfAbsent(item);
        }

        // Both should deduplicate to 4 unique tables
        assert defective.getOrdered().size() == 4
            : "Defective: expected 4 unique items, got " + defective.getOrdered().size();
        assert fixed.getOrdered().size() == 4
            : "Fixed: expected 4 unique items, got " + fixed.getOrdered().size();

        System.out.println("  [PASS] FK second-pass dedup (defective=" + defective.getOrdered().size()
            + " fixed=" + fixed.getOrdered().size() + ")");
    }

    static void testPerformance() {
        final int N = 5000;

        // Defective: O(n²) — each addColumn scans the whole list
        DefectiveConstraint defective = new DefectiveConstraint();
        long t0 = System.nanoTime();
        for (int i = 0; i < N; i++) {
            defective.addColumn("column_" + i);
        }
        // Re-add all to trigger the contains() scans on a full list
        for (int i = 0; i < N; i++) {
            defective.addColumn("column_" + i);
        }
        long defectiveNs = System.nanoTime() - t0;

        // Fixed: O(n) — LinkedHashSet add() is O(1)
        FixedConstraint fixed = new FixedConstraint();
        t0 = System.nanoTime();
        for (int i = 0; i < N; i++) {
            fixed.addColumn("column_" + i);
        }
        for (int i = 0; i < N; i++) {
            fixed.addColumn("column_" + i);
        }
        long fixedNs = System.nanoTime() - t0;

        double speedup = (double) defectiveNs / fixedNs;
        System.out.printf("  [PERF] N=%d  defective=%.1fms  fixed=%.1fms  speedup=%.1fx%n",
            N,
            defectiveNs / 1_000_000.0,
            fixedNs / 1_000_000.0,
            speedup);

        // Expect at least 5× speedup at N=5000 due to O(n²) vs O(n)
        assert speedup > 5.0
            : "Expected >5x speedup, got " + speedup + "x — fix may not be effective";
    }
}